Portable devices such as a smartphone, a tablet computer, a notebook computer and the like have been widespread. Such portable devices comprise a display device using liquid crystal, an organic electroluminescent element or the like. A display device comprises a microprocessor (also called a host device) configured to output pixel data, a command and the like and a driver configured to process the command and drive the display panel.
In a liquid crystal display device, pixels two-dimensionally arrayed on a display panel comprise common electrodes and pixel electrodes, and liquid crystal is sandwiched between the common electrodes and the pixel electrodes. A panel driver (also called a liquid crystal driver) can write a pixel signal to the pixels of the display panel. The liquid crystal between the common electrodes and the pixel electrodes is thereby controlled and an image is displayed.
The panel driver configured to supply a pixel signal to the pixels of the display panel generally comprises a frame memory. Pixel data from the outside is written to the frame memory. Pixel data corresponding to one horizontal line is sequentially read from the frame memory and converted into a pixel signal by analog conversion. The pixel signal is supplied to the pixels of the display panel.
The display device integrally comprises a touch detection system (also called a touchpanel). The touch detection system can detect a touch position in response to a touch of a user's finger, a stylus pen or the like on an icon or an operation button displayed on a display screen of the display device.
Recently, the touch detection system is configured such that a driving pulse for touch detection is supplied to the common electrodes. In the display device, operation for image display by the panel driver and operation for touch detection by the touch detection system are time-shared. For example, part of a display period of one frame is assigned for a touch detection period.